These attributes are printed in the "outputs" response, and the new
command "outputset" allows setting new values.
No attributes are currently implemented.
Coverity discovered that the Pulse plugin could throw exceptions from
Pause(), but that method was marked "noexcept" because its caller was
not designed to catch exceptions. So instead of avoiding exceptions
(by catching and logging them in each and every implementation), let's
allow them, and do the catch/log game in the MPD core.
Fixes regression from commit 31bad5f7af:
if Pause() returns true, the output thread is running a busy loop,
causing 100% CPU usage, instead of just closing the output.
Closes#105
